In the past, devices such as a battery charger has supplied electric power in non-contact state without directly connecting terminal pins to the terminal devices. An electromagnetic induction method is known as such past non-contact power supply transmission method. In this method, a device on an electric power transmission side is equipped with an electric power transmission coil, and a terminal device on a reception side is equipped with an electric power receiving coil. In this electromagnetic induction method, the location of the electric power transmission coil of the transmission-side device is arranged close to the location of the electric power receiving coil of the reception-side device, in order to bond magnetic flux between both coils to send electric power without contact.
Also, what is called a magnetic field resonance method is developed as a method for efficiently supplying electric power without contact to a terminal device which is a certain distance away. In this method, the device on the electric power transmission side and the device on the electric power receiving side are each equipped with a LC circuit consisting of coils and capacitors, which allows the electric field and the magnetic field to resonate between both circuits in order to transmit the electric power wirelessly.
In both of the electromagnetic induction method and the magnetic field resonance method, the device on the electric power transmission side is equipped with an electric power transmission coil, and the device on the electric power receiving side is equipped with an electric power receiving coil. When the electromagnetic induction method is referred to in the following present specification, the electromagnetic induction method also includes a similar non-contact power supply transmission methods such as the magnetic field resonance method.
FIG. 11 is a diagram illustrating an exemplary configuration of the past, which feeds power by the electromagnetic induction method without contact to a terminal device from an electric power feeding device. An electric power feeding device 10 as a primary-side device converts an alternating current power supply 11 such as AC 100V, to direct-current low-voltage power supply, with an AC-DC converter 12. The direct-current low-voltage power supply obtained by the AC-DC converter 12 is supplied to an electric power transmission driver 13. The electric power transmission driver 13 is connected to an electric power transmission circuit, which is connected to a capacitor 14 and a primary-side coil 15, and transmission electric power of a predetermined frequency is supplied from the electric power transmission driver 13 to the primary-side coil 15.
In a terminal device 20 as a secondary-side device, a secondary-side coil 21 and a capacitor 22 are connected to a rectifier unit 23, so that the secondary-side coil 21 receives electric power from the primary-side coil 15. The series circuit of the secondary-side coil 21 and the capacitor 22 is connected to the rectifier unit 23, so that the rectifier unit 23 rectifies the received power supply, to obtain direct current power supply of a predetermined voltage Va. The predetermined voltage Va is, for example, direct-current power that is slightly over 5V.
The direct current power supply obtained by the rectifier unit 23 is supplied to a regulator 24, and is regulated at a constant voltage (for example 5V). The direct current power supply of a constant voltage obtained by the regulator 24 is supplied to a charge control unit 25, and the charge control unit 25 controls charge of the secondary battery 26.
In such configuration of a non-contact electric power feeding system, the regulator 24 of the secondary-side device is a series regulator that is normally referred to as a low drop out (LDO), which is employed when the difference between an input voltage and an output voltage is relatively small. Using the LDO as the regulator 24 enables a system whose efficiency is high to a certain extent, for reception of electric power as low as about 5 W.
In the meantime, in the non-contact electric power transmission, the transmission electric power is desired to be increased. That is, in the current non-contact electric power feeding systems that has been put into practical use, the reception electric power in the terminal device is relatively small electric power of about 1 W to 5 W. In contrast, in the non-contact transmission by the electromagnetic induction method, the terminal device is desired to obtain larger reception electric power, such as 10 W and 15 W.
Here, when large electric power is received in the configuration illustrated in FIG. 11, the regulator 24 using the LDO has a problem of large loss at a coil where a large current flows.
A switching regulator that is called a DC-DC converter is known as a regulator that processes relatively large electric power and high voltage. Patent Literature 1 describes parallel use of a regulator using an LDO and a switching regulator in the power supply device. This Patent Literature 1 describes use of the switching regulator when the load is large, and use of the regulator with the LDO when the load is small.